A film preparation work station described and depicted in the above-incorporated '582 application is depicted in FIG. 1. An elongated film comprising spliced together developed filmstrips that have been separated from their cartridges is loaded into a film preparation work station 132. The work station 132 checks splice integrity, cleans the film and electronically scans the film to capture information used during the printing of both service prints (optical prints of developed images from the film onto photographic paper) and index prints. The work station is mechanically independent of associated service and index printers described in the '582 application.
The work station 132 includes supply and take-up reels 142 and 144, respectively, including appropriate drives and drags for removing slack and maintaining slight tension at the beginning and end of the film line. Film is unwound from its spliced roll 146 at supply reel 142, moves through a substantially straight line path 148, through a series of operating stations, and is wound up again into a reverse roll 150 at take-up reel 144. A metering roller 152 pulls the film along the straight line path around a capstan 154 and through the operating stations at a constant and controlled speed. In this Figure, the metering roller 152 and capstan roller 154 are shown schematically and not necessarily in the actual positions when implemented. The first station after roller 154 is a splice/perforation detector 156 that checks the integrity of the splices between the film strips and detects film perforations. A staple detector may also be included. Next is a film cleaner 158 for removing dust particles that would decrease the accuracy of the image scanning. A series of electronic scanning devices 160, 162 and 164 read or capture information from the film. A second splice detector 166 is positioned in this same series. The first electronic device 160 is an optional transducer called a film code reader (FCR). It captures a film identification (FID) that is applied as a latent image bar code (LIBC) when the film is manufactured. This latent image code is developed in the film processor 130, after which it is machine readable. The film identification is the same as the cartridge identification (CID), also applied as a machine readable bar code at the time of manufacture. The film identification (FID) captured here is printed on the back of each service and index print in subsequent printer operations.
The film code reader (FCR) 160 also identifies the beginning of each film strip, establishes the location of each image frame using the mark or perforation mentioned earlier in connection with the APS format, and looks for a FAT bit as described later in this section.
A magnetic read head assembly 162 that reads magnetically recorded information from a magnetics-on-film (MOF) layer of the individual filmstrips is positioned in the film transport path between the FCR 160 and the second splice detector 166. Some cameras using a film format as described further in the above-incorporated '582 application will record a variety of information in tracks of the MOF layer representing certain exposure conditions. Other pre-recorded information may be present in other tracks, and information related to the processing and printing event may be recorded in other tracks. Such filmstrips and the various types of magnetically recorded information, including the use or reproduction of the recorded information during film processing, are also described in commonly assigned U.S. Pat. No. 4,977,419.
Other cameras will not have magnetic recording capability but may have a capability for recording image format information, e.g. normal and panoramic format. Such image format information will be exposed on the individual filmstrip for that camera film as a latent bit referred to as a "FAT" bit. The information represented by the presence or absence of a FAT bit is captured in the work station by the FCR 160.
Station 164 includes an opto-electronic transducer or array scanner for electronically scanning and capturing representations of the developed images from the film. The electronic image representations are used to determine appropriate transfer densities and color correction factors for a service printer and for generating index prints in an index printer. The array scanner views the film through a full width slit while the film is pulled continuously over the slit by metering roller 152.
The magnetic read head assembly 162, when engaged, imposes drag on the film because the magnetic head or heads must make intimate contact with the MOF layer in order to accurately read out the information recorded in one or more tracks. The optically transparent MOF layer has a low magnetic particle density that requires such high head compliance, which creates the drag. Although not shown, it will be understood that a further MOF write head assembly may also be used in the film preparation work station positioned between the metering roller 152 and the take-up reel 144. In MOF read head assemblies 162 and write head assemblies considered for use in the film preparation work station, the drags imparted to the film vary from 9-11 oz.
The transport of such films through such a film preparation work station 132 is conducted at a steady velocity to accommodate the image frame scanning and MOF layer read out and recording. The film is longitudinally stiff and not subject to stretching. However, it can jam or break. Moreover, the movement of the supply and take-up reels 146, 144 tends to be uneven as the film may not wind uniformly on the reel hubs due to the intermittent splices.
In use of the film preparation work station 132, it is desired to be able to accurately move or advance the film at a constant velocity in either the forward direction or the rewind direction and to effect positioning of the film to a desired start position from any current position. In this process, imbalances in the tensions on the film must be minimized. A first tension appears on movement of the film in the film length between the supply reel and the metering roller, and a second tension appears on movement of the film in the film length between the metering roller and the take-up reel. As described further below, in the absence of correction, the first and second tensions are not equal and vary.
In the past, a wide variety of reel-to-reel web transport systems have been proposed for webs of various materials including paper, magnetic tape, motion picture film and spliced-together filmstrips. Control of tension in the web is of importance in a variety of contexts. A common approach involves the use of variable length, tension loops as disclosed in U.S. Pat. No. 5,039,027, for example, for measuring tension between a metering roller and the supply and take-up reels. The use of such tension loops is particularly useful in controlling web tension during acceleration and deceleration in a single direction of web transport.
Problems to be Solved by the Invention
Such tension loops complicate the threading of webs from the supply to the take-up reel. It is desirable to provide simple automatic threading of the web or film between the supply and take-up reels. Traditional tension loops are overly complex, requiring three additional idler rollers, springs, bearings and feedback devices, such as potentiometers. A servo loop is typically required for maintaining constant tension in these loops and it is difficult to stabilize over a wide range of differing film sizes (e.g. 35 mm and 24 mm), film cores and winding diameter inertias. In addition, the mechanism that would be required to compensate for tension drops due to the drags imposed by additional devices in the film transport path would be overly complex and expensive.